1. Field of the Invention
The present invention relates to a tape cassette type discrimination apparatus and, more particularly, to a tape cassette type discrimination apparatus in a magnetic recording/reproducing apparatus such as a VHS video tape recorder, to which general and special type tape cassettes are loaded.
2. Description of the Related Art
Some conventional VHS video tape recorders (to be abbreviated to as VTRs hereinafter) have a function of discriminating a type of a tape cassette loaded in the VTR. The tape cassette is of a general type, and has an apparatus for discriminating the type of tape of the tape cassette. The apparatus detects a discrimination corresponding to the type of a tape to determine the (length) and hub diameter of the tape include T-20, T-30, T-40, T-60 and tapes having a small-diameter hub include T-80, T-90, T-100, T-120, T-140, T-160, and obtains a discrimination value inherent to the type of type to discriminate the type of tape. An example such as discrimination apparatus is disclosed in, e.g., Japanese Patent Disclosure (Kokai) Nos. 54-145513 and 58-29156. In the tape-type discrimination apparatus, if a rotational angular velocity of a supply reel is given by W.sub.S ; a rotational angular velocity of a take-up reel, W.sub.T ; a tape travel speed, V; the radius of a winding diameter of the supply reel, r.sub.S ; the radius of a winding diameter of the take-up reel, R.sub.T ; the radius of a hub diameter, R.sub.O ; the length of the tape, L; the thickness of the tape, d; the tape winding area of the supply reel, S.sub.S ; and the tape winding area of the take-up reel, S.sub.T, the following relations are established: EQU r.sub.S W.sub.S =r.sub.T W.sub.T =V (1) EQU S.sub.S -.pi.(r.sub.S.sup.2 -R.sub.0.sup.2) (2) EQU S.sub.T -.pi.(r.sub.T.sup.2 -R.sub.0.sup.2) (3)
From equations (2) and (3); ##EQU1## More specifically, according to equation (5), the value of r.sub.S.sup.2 +r.sub.T.sup.2 is calculated to discriminate the type of tape. The discrimination result is used as data for detecting a tape position or tape remaining amount. More specifically, the tape position can be calculated from the above-mentioned equations (1) to (3). However, numerical values of a hub diameter, tape length, and tape thickness of the cassette are required as data for the arithmetic operation. These values vary depending on the types of cassette. Thus, these values are prestored in an accumulation means, and are read out and used in accordance with a cassette discrimination result. For example, detection of an actual tape position can utilize the known technique described in U.S. Pat. No. 4,172,231.
The amount of tape remaining can be obtained based on the tape position information as a result of the arithmetic operation and the tape length data, and tape transit control can be performed according to a tape position using the tape position information. For example, in a FF (fast-forward) or REW (rewind) mode, a tape end can be reliably detected to stop tape movement.
In the tape-type discrimination apparatus described above, when a compact cassette adapter in which a special type cassette having a smaller size (VHS-C cassette; referred to as a C-cassette hereinafter) is loaded in place of a general type tape cassette (normal VHS cassette; to be referred to as a VHS cassette hereinafter), it is difficult to determine that the type of the tape cassette is different. More specifically, the C-cassette adapter has different hub diameters at supply and take-up sides. In addition, rotation of a take-up drive unit of the C-cassette and rotation of the take-up reel of the adapter are different, e.g., have a rotation ratio of 2.34:1. For this reason, when the C-cassette adapter is loaded in a VTR, a special value inherent to the C-cassette adapter appears at a data top (in a state wherein almost no tape is taken up to a take-up side). However, at a data end (in a state wherein almost no tape is present at a supply side), a specific value of a VHS cassette having a small-diameter hub appears.
For this reason, when a tape is driven with the same driving means as is used for a normal VHS cassette, a rotation ratio of rotation of the take-up reel of the C-cassette adapter to that of the take-up drive unit of the C-cassette is 1:2.34. For this reason, when the C-cassette adapter is driven, a tape travel speed is slightly increased, and more tape tends to be taken up at an end portion of the tape. In order to solve this problem, the tape travel speed may be decreased at the tape end portion of the C-cassette adapter. However, in the method of decreasing the tape travel speed, when a normal tape cassette is loaded and driven, a tape take-up time is prolonged, and a tape cannot be uniformly wound.